One undifferentiated spares list produces both overstock and eight-week line-down events. Splitting spares into three categories with different rules fixes most of it.
Most plants keep one spares list, and it fails in both directions at once: capital tied up in parts that will never be fitted, alongside a line-down event waiting on an eight-week lead time. The problem is not the stock level. It is that one list, one rule, is being asked to cover parts with completely different risk profiles.
List one is line-down spares: parts whose failure stops production and cannot be sourced within your tolerable downtime. Main PLC, drives, the special gearbox, the non-standard sensor. The rule here is unconditional — hold them on the shelf, on site or under a guaranteed-availability agreement, and treat the cost as insurance premium, not inventory.
List two is wear parts with predictable consumption: contactors, belts, seals, filters, tooling. These are a scheduling problem, not a risk problem. Set minimum and reorder quantities from actual consumption history and let normal purchasing run them. The only failure mode here is nobody updating the numbers after a line speed change.
List three is the obsolescence watch list: parts still available today whose manufacturers have signalled the end. This list only works if someone owns it — reviewing discontinuation notices against the installed base once or twice a year and converting each hit into a decision: last-time-buy, approved substitute, or planned retrofit. Unowned, the list is just a spreadsheet with a countdown nobody is watching.
The precondition for all three lists is knowing what is actually installed. Panels drift from their drawings over twenty years of repairs, and a spares strategy built on original documentation covers the plant you commissioned, not the plant you run. We start every spares engagement with an as-built survey for exactly this reason.
None of this requires software beyond what the plant already has. It requires the classification, the ownership and the annual review. Two working days per year against the cost of one uncovered line-down event is not a difficult business case to write.
— GANI Lifecycle engineering team